ROTATION OF CROPS. 205 



growth under the influence of each of the manures, are 

 strikingly illustrated, both by the figures and by the amounts 

 of produce given. Indeed, the results conclusively show Abundance 

 how artificial a product is the cultivated root-crop, and how j^XSi? 

 dependent it is for its successful growth on an abundant tiai/or 

 supply of available food — nitrogenous as well as mineral — turnips. 

 within the soil. 



The Barley Crops. 



Table 57 (p. 206) gives the produce of barley, the second 

 crop of the course, and therefore always succeeding the roots, 

 in each of the eleven years in which it was grown, in precisely 

 the same form as that of the Swedish turnips recorded in Tdblebi 

 Table 56 : the upper division giving the grain per acre, the ex P lained - 

 middle division the straw, and the lower one the total pro- 

 duce, grain and straw together. 



As in the case of the root-crops, so in that of the barley, 

 the produce in the first course is excluded from the calcula- 

 tion of the averages to which reference will chiefly be made. 

 Indeed, the results of the first year of barley confirm the 

 conclusion that the land was in somewhat high condition 

 due to recent accumulations. The produce of the tenth and 

 eleventh courses is also excluded from the averages, on 

 account of the change of manure on the superphosphate plot 

 for the tenth and succeeding courses. 



Referring, however, first to the results of each of the eleven Variation 

 years, it is seen that, under each condition of manuring, or J^ M# 

 other treatment, there is very great variation in the amount 

 of produce from year to year, due to variations in the 

 characters of the seasons. Thus, without manure, the 

 average produce over the eight courses was about 30 bushels 

 per acre, whilst in 1857 it was in each case more than 40 

 bushels, and in some considerably more ; but in 1869 and in 

 1873 it was not much over 20 bushels, and in the last two 

 courses considerably less than 20. A glance down the 

 columns recording the produce on the manured plots will 

 show that in their case also there was a wide range in amount 

 above and below the averages, according to season. 



Referring now to the average produce of the eight courses 

 (second to ninth), the first point to notice is, that whilst the 

 assumed restorative crop — the roots — gave practically no 

 produce at all without manure, the barley gave, on land un- No man- 

 manured for so many years, an average of rather over 30 ure - 

 bushels per acre. The truth is that the cultivation for the 

 preceding roots kept the land clean, and as there was prac- 

 tically no produce of roots, the soil was, in point of fact, left 

 almost fallow for the barley during the winter preceding the 



